The disclosed invention generally relates to center high mounted brake lights or stoplights for vehicles, and more particularly is directed to a center high mounted stoplight assembly which includes a scatter blocking holographic structure for preventing scattered stoplight illumination from being viewable in the rearward field of view of the vehicle operator.
Present Federal regulations require center high mounted stoplights in automobiles in addition to the traditional stoplights. The high mounted stoplights are intended to maximize the visibility of the stoplights to following drivers.
Center high mounted stoplights have been implemented as a standard lenticular lens and an illuminating incandescent bulb enclosed in a housing that is commonly secured adjacent the top or bottom of an automobile rear window (also referred to as an automobile backlight). The bulky housing, which is intended to prevent scattered stoplight illumination from being within the driver's rearward field of view, partially obscures rearward visibility, imposes limitations on design, and is generally unattractive. Further, the bulky housing can create the startling impression that a vehicle is following close behind. And although the bulky housing is intended to prevent scattered stoplight illumination from entering the automobile, it is not completely effective, particularly if the backlight is dirty and/or covered with moisture or snow.
In order to avoid the visibility obscuration of the bulb and lens center high mounted stoplight, holographic stoplight systems have been developed wherein holograms secured to the automobile backlight provide stoplight illumination when illuminated with playback illumination. The holograms are substantially transparent to the driver's rearward field of view, and the playback illumination source is outside such field of view, which avoids the obscuration presented by the bulb and lens type stoplight assemblies. Examples of center high mounted holographic stoplights are disclosed in U.S. Pat. No. 4,892,369, for "Holographic Rear Window Stoplight," which is assigned to assignee of the subject application.
However, holographic stoplight systems, like the bulb and lens type stoplight assemblies, produce unwanted scattering into the automobile of stoplight illumination when the backlight is dirty and/or covered with moisture or snow. Further, recording imperfections and recording material properties cause the hologram itself to scatter playback illumination into the automobile.
The forward scattering of stoplight playback and imaging illumination may be sufficiently intense as to be unacceptable unless the stoplight illumination intensity is reduced, which may result in an unacceptably low intensity.